STUDIES ON BIOSYNTHESIS OF PROTEIN AND LIPID COMPONENTS OF RAT LIVER MITOCHONDRIA

Male rats were injected intraperitoneally with L-[35S]methionine, [32P]phosphate and [2-14c] acetate. The animals were killed at various times up to 72 hr. after injection, and liver mitochondria were prepared and fractionated into soluble protein, insoluble protein and lipid for assay of the radioactivity of each fraction. The maximal specific radioactivity of total mitochon-drial phospholipid with respect to both 32P and 14c was attained after approx. 6 hr. 32p was incorporated most rapidly into phosphatidyl-ethanolamine, maximal incorporation being attained after approx. 6hr., maximal incorporation into lecithin occurred after 6-12 hr. The specific radioactivity of cardiolipin was still slowly increasing at the end of the experiment (72 hr.) There were no major differences between rates of incorporation of 14c into the lecithin, phosphatidyl-ethanolamine and cardiohpin fractions of mitochondrial phosphospholipid, maximal incorporation in each case occurring after approx. 6 hr. Maximal incorporation of 35S into both soluble and insoluble protein fraction was attained less than 12 hr. after injection, the maximal specific radioactivity of soluble protein being higher than that of insoluble protein.